2 channel bio amplifier

Session T3F

978-1-61284-469-5/11/$26.00 2011 IEEE October 12-15, 2011, Rapid City, SD

41st ASEE/IEEE Frontiers in Education Conference

T3F-1

A Two-Channel Bioamplifier Design

as a Cross-Course Experience

Steve Warren, James DeVault, and Kejia Li

Kansas State University, Electrical & Computer Engineering, 2061 Rathbone Hall, Manhattan, KS 66506 USA

Phone: (785) 5325600, Fax: (785) 5321188, Email: [email protected], [email protected], and [email protected]

Abstract A cross-course design experience is an efficient way to stitch together two concurrent, single-

semester courses to obtain a meaningful number of

design credits without unduly increasing a students overall load. This paper addresses a project that joined

the design credits from two Kansas State University

(KSU) courses: ECE 773 Bioinstrumentation Design Laboratory and ECE 502 Electronics Laboratory. The goal of each project team was to design, build, and

demonstrate a two-channel bioamplifier that is

functionally similar to a commercial bioamplifier used in

the KSU AP 773 Bioinstrumentation Laboratory course taken by some of these students. Assessment of the

experience was provided via a post-project survey that

addressed eight learning objectives, learning in 23

technical areas, project administration, and the overall

experience. Survey results were positive across the

board. Though the time commitment was significant,

the students appreciated the opportunity to work on a

complex system that required their collective expertise.

Index Terms Amplifiers, biomedical instrumentation, biosignals, capstone design, filters, team work

I. INTRODUCTION

A. Motivation

Hands-on design experiences are emphasized by ABET

Inc. through the requirement that senior capstone design

experiences be incorporated into ABET-accredited curricula

[1]. Faculty generally agree that such experiences offer

more in-depth learning when compared to traditional

lectures and scripted laboratories. The KSU Department of

Electrical & Computer Engineering (ECE) [2] offers

undergraduate curricula consistent with that theme.

In a single-semester course that offers both lecture and

design components, an instructor can find it difficult to

address the lecture material and still retain enough course

time to guide a substantive design effort. A cross-course

design experience is therefore an efficient way to stitch two

such courses together to increase the aggregate number of

design credits for a given project without unduly increasing

an individual students overall load [3]. An added benefit of this approach is that each course can inform the other,

enriching students experiences by supplying context that may have otherwise been lacking [4, 5] or merging the

elements of design and analysis in a more meaningful way

[6-8]. These thoughts motivated the cross-course project

presented here an effort that joined the Fall 2009 design credits associated with two concurrent courses: ECE 773 Bioinstrumentation Design Laboratory and ECE 502 Electronics Laboratory. The two-fold goal was to increase

the number of design credits and provide a biomedical

context for an otherwise generic design experience. Fig. 1

depicts the participating students/faculty.

FIGURE 1

PARTICIPANTS IN THE CROSS-COURSE DESIGN EXPERIENCE

B. Course Descriptions

ECE 773 Bioinstrumentation Design Laboratory (1 hour) is a required single-semester design course for KSU

Electrical Engineering (EE) seniors enrolled in the

Bioengineering Option. This course is a co-requisite to

ECE 772 Bioinstrumentation Lecture (2 hours) and AP 773 Bioinstrumentation Laboratory (1 hour), a course pair also offered to upper-level students in non-EE curricula [9].

The courses address biomedical sensors, biomedical signals,

instrumentation, computer-based data acquisition, and

medical imaging. Students work in teams to develop

sensor-based systems that acquire, process, and display

health monitoring data. ECE 502 Electronics Laboratory (2 hours) is a junior-

level, single-semester laboratory required for all KSU EE

students. Topics include operational amplifier applications,

large- and small-signal amplifier performance testing,

analog filters, and analog-to-digital (A/D) (and digital-to-

analog (D/A)) conversion. Students enter this course with

diverse skill sets, so early-semester activities incrementally

progress from a completely specified exercise to an open-

ended experiment requiring a student-designed procedure.

The final third of the semester is dedicated to team projects.

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II. METHODOLOGY

A. Brief Project Description

The goal of this project was to design, build, and

demonstrate a two-channel bioamplifier (biomedical signal

amplifier) that is functionally similar to the iWorx ETH-255

Bioamplifier [10] depicted in Fig. 2. Each channel was to

provide pre-amplification signal offsets, four amplifier gain

settings, allpass/lowpass/highpass/notch filters that operate

in cascade, and electrical isolation between a sensor and the

bioamplifier circuitry. The unit needed to incorporate a

plug-in power adapter, standard connector support, a power-

on indicator, control knobs, and an enclosure. End-of-

semester deliverables included team presentations, hardware

demonstrations, and user manuals.

B. Learning Objectives

This project supported eight learning objectives that

took the following form: Upon completion of this project, team members should be able to

1. Describe the role of biosignal amplification and filtering circuitry in a real world context

2. Acquire physiologic data with biomedical sensors 3. Partition the design of a biosignal amplifier into

smaller, more manageable units

4. Condition biomedical signals to remove noise and other unwanted signal components

5. Describe the tradeoffs encountered when designing filters that exhibit lowpass, highpass, bandpass, and

bandstop characteristics

6. Document the features of a bioamplifier and instruct others in its use

7. Match team members to project areas that utilize their interests and skills

8. Work more effectively with individuals having different areas of expertise

C. Bioamplifier Requirements

Each bioamplifier was to demonstrate the following

specific features/functionality:

Two input/output signal channels

DIN-8 connectors for the input signal cables

Coaxial connectors for the output signals

Wall wart transformer for bioamplifier power, using a standard power jack

LED power-on indicator

Knobs to control signal offsets, gains, and filter cutoff frequencies

Input signal offsets that operate prior to signal amplification and/or filtering

Signal gains of 1, 10, 100, and 1000

Lowpass, highpass, bandpass, and bandstop filters that can operate in cascade

Lowpass filter cutoffs: 4/50/150/2000 Hz plus wideband

Highpass filter cutoffs of 0/0.1/3 Hz

60/120 Hz bandstop filters engaged or bypassed with a switch or push button

Electrical isolation (signal and power) between the sensor and the amplification/filtering circuitry

D. Project Administration

Students enrolled in the Fall semester of ECE 773

(seven students) and ECE 502 (21 students) were divided

into five teams, each of which designed a two-channel

bioamplifier (three students were enrolled in both courses).

The five team leaders (and two co-leaders) were chosen

from the ECE 773 student pool with the thought that their

additional experience with biomedical devices would help

them to better define the bioamplifier requirements for the

signals of interest: electrocardiograms, plethysmograms,

electromyograms, and other traditional biomedical

waveforms. Additionally, most of these students had

already taken ECE 502 as part of their required EE

curriculum, so they were already familiar with some of the

subject areas to be addressed during the project. For part of

their ECE 773 credit, team leaders negotiated design roles,

submitted weekly updates to the instructors, and collated

material for user manuals and presentations.

Responsibilities for a five-member team were typically

aligned with these design areas: (1) power supply, (2)

isolation amplifier, (3) filters and offsets, (4) switching, and

(5) physical connections and case. The signal visualization

method was discretionary. To save time, each team

prototyped circuitry on breadboards, created a wire-wrapped

version of the final designs, and then housed the circuitry in

a case. Cases, buttons, and parts were provided by KSU

ECE. The team with the overall best design was given the

option to construct printed-circuit-board versions of their

bioamplifier to be displayed during the Spring 2010 KSU

Open House, where the intent was to use that design in

subsequent course offerings.

E. Deliverables

Bioamplifier operation was demonstrated with signals

from a CB Sciences C-ISO-255 electrocardiograph (see

Figure 2A) and an iWorx pulse plethysmograph (see Figure

2A); these devices incorporate DIN-8 connectors (see

Figure 2D). Each team assessed tradeoffs between at least

two designs for each filter type. They were also required to

create a user manual for their device that incorporates sub-

system descriptions, experimental transfer functions for all

filter settings, filter tradeoffs, references, and operating

instructions. Bioamplifier designs were presented during

the scheduled ECE 773 final exam period.

F. End-of-Semester Assessment Surveys

Surveys recorded student perceptions of learning, tallied

project elements that students liked/disliked, and archived

suggested project improvements. Survey results are listed

and discussed in the next section.

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T3F-3

FIGURE 2 IWORX ETH-255 BIOAMPLIFIER: A BIOAMPLIFIER, CB SCIENCES C-ISO-255 ELECTROCARDIOGRAPH, AND IWORX PULSE PLETHYSMOGRAPH;

B ETH-255 FRONT PANEL; C ETH-255 BACK PANEL; D DIN-8 CONNECTOR

III. RESULTS & DISCUSSION

A. Student Design Products

The project was substantial given end-of-semester time

constraints, but all five teams demonstrated functional units.

High-level signal flow and switching approaches varied, as

illustrated in Figs. 3 and 4. Further, each group designed its

front and back panel layouts differently; an example is

depicted in Fig. 5. Most of the lowpass and highpass filter

designs were traditional (e.g., an 8th

-order Butterworth filter

constructed from a cascade of 2nd

-order Sallen-Key filters),

whereas the 60 Hz notch filters demonstrated variety. Final

products were relatively complex and in some cases quite

impressive. Two of the final designs are pictured in Fig. 6.

FIGURE 3

SIGNAL FLOW DIAGRAMS FROM TWO DESIGN TEAMS (GROUP A: TOP; GROUP E: BOTTOM)

FIGURE 4

SIGNAL FLOW AND SWITCHING (GROUP D)

Front Panel

Rear Panel

FIGURE 5

EXAMPLE FRONT AND BACK PANEL LAYOUTS (GROUP B)

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T3F-4

FIGURE 6 FINAL BIOAMPLIFIER DESIGNS FROM TWO DESIGN TEAMS

B. Student Survey Results

The first two survey elements (Tables I and II)

addressed project learning objectives and technical areas. In

these tables, the Pre and Post columns represent student perceptions of their comfort and proficiency before and after

the project, respectively. The column represents the average difference between those pre- and post-project

ratings.) Numbers represent averages for the entire set of

participants. While roles were initially mapped to specific

learning objectives and technical areas, those data were not

tallied separately, since each student contributed to areas

outside of their role. The third survey element (Table III)

sought project opinions. Open-ended questions followed:

What part of the project did you like the most?

What part of the project was your least favorite? Did you have any general frustrations?

In retrospect, would have you done anything differently between the time the project was assigned and the

submission deadline?

How could a project of this nature be improved?

What other general comments come to mind? Finally, experience reveals that some students ride along given contributions of capable teammates, completing a

degree while lacking in essential skills. The survey

elements in Table IV were appended to more realistically

assess the contributions of individual team members within

the overall scope of the project.

C. Survey Interpretation

Learning Objectives Survey. After an assessment of

user manuals and presentations/slides, the project learning

objectives were clearly met in aggregate. This is confirmed

by the student self assessments in Table I. In each area, the

students comfort level increased between project onset and completion. The most improvement was noted on objectives

1, 3, 4, and 6, which address facets of these amplifiers and

filters that are directly related to the characteristics of

biomedical signals; quantities not normally addressed in the

core EE curriculum outside of the EE Bioengineering

Option. Moderate improvement was noted on objectives 3

and 5. The sensors used by the students were off-the-shelf

units that simply needed to be plugged into the amplifier, so

objective 3 did not get much attention. The design of a third

sensor from scratch was originally included in the project

description (and would have helped with objective 3), but it

was removed as a means to lessen the student time

commitment. Regarding objective 5, these students had

already been introduced to filter tradeoffs in multiple lecture

and laboratory contexts, so only moderate learning was

anticipated. The least improvement was seen in objectives

78. First, the students were primarily self-selective regarding team tasks, so matching of expertise and skills

was not practiced. Second, most of these students skill sets were consistent from student to student, as they had all

progressed through the same curriculum, leading to minimal

learning regarding multidisciplinary team efforts.

Technical Proficiency Survey. As expected, the

technical areas that demonstrated the largest increase in

perceived proficiency were those that were initially the least

familiar to the students but required attention to achieve a

working system: biomedical sensor interfacing, DIN-8

connector use, electrical isolation, wire wrapping, and

biomedical signal conditioning. Moderate proficiency gains

(s in the range of (1.4, 1.8)) were experienced in the areas of signal offset circuitry, notch filter design, filter cascades,

switching, and enclosure design.

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TABLE I

LEARNING OBJECTIVES SURVEY

On a scale of 1 to 5, note your comfort level with these learning objectives,

where 1 means no comfort and 5 means high confidence. Respond to all objectives, even those that did not relate directly to your project role(s).

LEARNING OBJECTIVE PRE Post

1. Describe the role of biosignal amplification/ filtering circuitry in a real world context

2.2 4.2 2.1

2. Acquire physiologic data with biomedical sensors 2.1 3.5 1.5

3. Partition the design of a biosignal amplifier into smaller, more manageable units

2.4 4.4 2.0

4. Condition biomedical signals to remove noise and other unwanted signal components

2.1 4.2 2.1

5. Describe the tradeoffs encountered when designing filters that exhibit lowpass, highpass,

bandpass, and bandstop characteristics

2.3 4.2 1.8

6. Document the features of a bioamplifier and instruct others in its use

1.8 4.1 2.3

7. Match team members to project areas that utilize their interests and skills

3.1 3.8 0.7

8. Work more effectively with individuals having different areas of expertise

3.3 4.0 0.8

TABLE II

TECHNICAL PROFICIENCY SURVEY

This project addressed various facets of bioamplifier design. On a scale of 1 to 5, note your proficiency/understanding level in these areas, where a

1 denotes no proficiency and a 5 denotes a solid understanding.

TECHNICAL AREA PRE Post

Biomedical sensor interfacing and application 1.6 3.6 1.9

DIN-8 connector use 1.5 3.6 2.1

BNC output connectors 2.2 3.4 1.2

Electrical isolation 1.5 3.7 2.2

Power conversion from a wall outlet 2.7 3.8 1.1

Battery-controlled sub-circuit operation (if used)

2.5 3.8 1.2

Instrumentation amplifier usage/design 3.1 4.0 1.0

Signal offset circuitry 2.9 4.3 1.4

Gain circuitry 3.9 4.4 0.5

Lowpass filter design 3.2 4.2 1.0

Highpass filter design 3.2 4.3 1.1

Notch filter design 2.4 3.9 1.5

Filter cascades 2.5 4.2 1.7

Physical switch usage 2.7 4.3 1.5

Gain and cutoff frequency switching issues 2.5 4.0 1.5

LED indicator application 3.3 4.2 1.0

Electronic component selection 3.0 4.1 1.1

Board layout 2.7 4.0 1.3

Wire wrapping 1.1 4.1 3.0

Enclosure design/layout 2.3 3.7 1.4

Circuit simulation tools 3.7 4.2 0.5

Source separation into signal and artifact 2.0 3.1 1.0

Biosignal conditioning in general 1.7 3.8 2.0

TABLE III

OVERALL EXPERIENCE SURVEY

ITEM VAL

Percentage of the planned amplifier functionality that your team was able to successfully implement (1 = 20%, 2 = 40%, etc.)

4.2

Your personal level of interest in the material

(1 = no interest, 5 = extreme interest) 4.1

Level of effort required by the team (1 = too little; 5 = too much) 4.0

Level of effort required by yourself (1 = too little; 5 = too much) 4.0

Access to instructor/TA assistance (1 = nonexistent; 5 = ideal) 3.6

Weekly discussions & design reviews (1 = no help; 5 = effective) 3.3

Hardware/software resources and facilities provided to enable the completion of your project (1 = inadequate; 5 = perfect)

4.3

TABLE IV

SELF AND TEAM MEMBER ASSESSMENT SURVEY

Each team member ideally contributed to a specific area of the project.

Please rate the contributions of your fellow team members in the following

categories. These data will be used to supplement observations made by the instructors and will remain confidential.

Categories

1. Amount of effort put forth by the student (1 = too little; 5 = too much) 2. Amount of effort expected of them given their project role (1 = none;

5 = too much) 3. Effectiveness of their technical contribution (1 = minimal; 5 =

indispensable)

4. Their contribution to team dynamics (1 = harmful; 3 = neutral; 5 = positive)

5. Their availability, proactivity, and reliability (1 = minimal; 5 = tremendous)

If you did not interact with a person enough to provide a reasonable rating

for their contribution in a given category, simply place an X in the corresponding box.

STUDENT TECHNICAL

CONTRIBUTION AREA

CATEGORY

1 2 3 4 5 6

Overall Experience Survey. This survey indicated that

students were able to implement most of the planned board

functionality and that they found the experience to be

interesting. Students reported that the project required a lot

of work, with the implication that better access to instructor

help would have been desirable. Lackluster responses to the

design reviews imply an area of focus in future offerings.

Open-Ended Questions. As in most survey instruments,

the open-ended questions yielded the most interesting and

useful data. When students were asked what they liked the

most, many of their responses (13 of 34, or 38.2%) focused

on the building process and the coming together of the

separate components to form the overall system. This

included the team interactions that made the consolidation

possible. With respect to technical subjects, the areas of

instrumentation (including filter design) and wire-wrapping

each received 5 of 34 responses (14.7%). The general area

of design, troubleshooting, and hands-on work also received

6 responses (17.6%). The work with the power supply,

case, and new design tools were also of minor note.

When asked what they liked the least, student responses

(11 of 26, or 42.3%) centered on the integration of a system

of disjoint, wire-wrapped pieces that was awkward to

integrate and debug. The process would take hours, leading

to a secondary theme noted by the students: the lack of time

needed to complete the assignment (4 of 26, or 15.4%).

Other complaints (5 of 26, or 19.2%) spoke to team

dynamics, including variations in participation level, a

desire for team unity, poor team communication, and

unnamed problems. While these latter issues could be

negatively construed, the instructors were glad these

responses emerged, since their presence meant that the

project exposed students to practical team issues they will

face as practicing engineers.

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T3F-6

When the students considered what they would do

differently, most of their responses (20 of 28, or 71.4%)

addressed better management of time and processes. This

included starting earlier, improved layout planning, better

sub-circuit test procedures, increased time allocation for

system assembly, better use of interim deadlines, earlier

emphasis on the power supply, and breadboard builds prior

to wire wrapping. Two students stated that they would not

have done anything differently on this project.

In terms of suggested project improvements, student

responses (16 out of 30, or 53.3%) centered on an earlier

start to the project. Other suggestions were varied and

included the following: a smaller-scale project to wire wrap

prior to the effort, a single channel instead of two, a PCB

design for the interior board(s), better component

availability (resistors and capacitors), a larger case, clear

responsibility mapping to team members, static project

specifications, more background information on the

biomedical signals, and filter cascade dialogue.

A number of general comments (7 of 15, or 46.7%) put

the project in a positive light, praising the effort as one of

the most complicated, interesting, and informative projects

these students have addressed in their undergraduate

curriculum. Even in light of the minor challenges, the

project was construed as an excellent hands-on learning

opportunity and a good real-world application: a welcome

alternative to a simulated system exercise. Negative general

comments that were offered dealt primarily with team

dynamics: over-controlling project leaders, struggles with

meeting times, and dissatisfaction with technical

assignments. It is worth noting that these latter comments

were so infrequent as to be almost anecdotal.

IV. CONCLUSION

This paper presented a cross-course design project that

merged physiological parameter and sensor concepts from a

biomedical instrumentation course with analog filter and

hardware assembly concepts from a generic electronics

laboratory course. The primary goals of this experience

were to (1) merge projects from two courses to create an

overall more substantive design experience and (2) lend a

biomedical context to an otherwise generic design project

that would direct students toward the idea of design with

clear societal benefit. The instructors consider this effort a

successful learning experience based on informal student

feedback, data accumulated from post-project surveys, the

quality of the user manuals, and the functional hardware

designed by the various student groups. While the project

itself required more overall work than a typical project

would require in either of the constituent individual courses,

the students found it satisfying to work in groups to create

more complex, tangible projects that benefitted from the

varied talents represented on each team.

ACKNOWLEDGEMENTS

The authors thank Steve Booth, KSU ECE, for his

assistance with the parts and cases needed for this project.

The authors also acknowledge the team members that

provided some of the content for the figures in this paper:

Group A Cody Barthuly, Jeremy Harris, Jack Plummer, Tanner Reynolds, and Alex Silva

Group B Jeff Schuler, Brian Tierney, Channing Navis, Faleh Alskran, and Adam Frakes

Group C Chris Newlin, Aaron Ortbals, Shwan Alkhatib, and Dana Gude

Group D Jim Groening, John Hill, Derek Brown, Luke Stauffer, and MHammad Lershaid

Group E Adriann Sullivan, Riley Harrington, Cochise Fant, Devon Krenzel, and Aaron Snuffer

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2 channel bio amplifier

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